1. Field of the Invention
The present invention relates to a polyphase electric motor, more particularly for applications for driving pumps or ventilators in the automobile industry.
In the industrial and automobile fields, the selection of a polyphase motor for driving pumps or ventilators is made, depending on criteria which can be cost, performances and lifetime criteria. As regards the performances, the output and noise are more particularly estimated. To reach a good output, it is necessary to have a sufficient volume of copper to emit the resistive losses and a short magnetic circuit to minimise the iron losses. To reduce the level of noise as much as possible, a correct balance of the radial forces as well as a low detent torque will be aimed at. The cost of the motor is related to the cost of materials but also to the cost of the manufacturing and it is particularly important to provide an economical solution for the manufacturing of the coil winding.
2. Description of Related Art
Motors are known in the state of the art, such as described in the German patent DE19905748, exhibiting a correct balance of the radial forces but the structure of such motors does not allow a simple manufacturing of the coil winding by separately winding the coils and by inserting them into the stator. As a matter of fact, mastering the detent torque requires poles having as wide as possible a shape, in such motors, and the coil winding must be made by inserting the copper wire through particularly narrow cut-outs. In order to make the coil winding easier, certain motors thus exhibit a stator made of several parts, but the simplification of the coil winding is thus at the expense of the design of the statoric circuit which becomes complex because of this assembling of such a large number of pieces and thus it becomes costly.
Motors are also known in the state of the art, which make it possible to reach a particularly simple and economical manufacturing of the coil winding on a stator made in one piece while providing a low detent torque. However, such motors are not totally balanced as regards the radial forces, which is a disadvantage as regards noise and also as regards the bearing lifetime. Such motors are for example described in the American patent U.S. Pat. No. 5,880,551 also assigned to the applicant.